linux-kernel - Re: [PATCH] drm/msm/dsi/dsi_phy_10nm: Fix missing initial VCO rate

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <ybbyhri7vydiyowr3iqrizefblrfpedk5it723o254vyklcd5c@cdx7rhx2f3rn>
Date: Wed, 21 May 2025 15:59:40 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Rob Clark <robdclark@...il.com>, Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dsi/dsi_phy_10nm: Fix missing initial VCO rate

On Wed, May 21, 2025 at 08:09:14AM +0200, Krzysztof Kozlowski wrote:
> On 20/05/2025 22:06, Dmitry Baryshkov wrote:
> > On Tue, May 20, 2025 at 01:13:26PM +0200, Krzysztof Kozlowski wrote:
> >> Driver unconditionally saves current state on first init in
> >> dsi_pll_10nm_init(), but does not save the VCO rate, only some of the
> >> divider registers.  The state is then restored during probe/enable via
> >> msm_dsi_phy_enable() -> msm_dsi_phy_pll_restore_state() ->
> >> dsi_10nm_pll_restore_state().
> >>
> >> Restoring calls dsi_pll_10nm_vco_set_rate() with
> >> pll_10nm->vco_current_rate=0, which basically overwrites existing rate of
> >> VCO and messes with clock hierarchy, by setting frequency to 0 to clock
> >> tree.  This makes anyway little sense - VCO rate was not saved, so
> >> should not be restored.
> >>
> >> If PLL was not configured configure it to minimum rate to avoid glitches
> >> and configuring entire in clock hierarchy to 0 Hz.
> >>
> >> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> >> Link: https://lore.kernel.org/r/sz4kbwy5nwsebgf64ia7uq4ee7wbsa5uy3xmlqwcstsbntzcov@ew3dcyjdzmi2/
> >> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> > 
> > Fixes?
> 
> Probably:
> Fixes: a4ccc37693a2 ("drm/msm/dsi_pll_10nm: restore VCO rate during
> restore_state")

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>

> But CC stable would not be appropriate, since this was never reproduced
> on this PHY/hardware and we only guess a visible issue being fixed here.

Agreed.

-- 
With best wishes
Dmitry